Chapter 9 Coordination Chemistry Structures and Isomers

What is Coordination Chemistry

• Cooordination Complex

– Central atom usually a d-block metal or ion

– Attach to the central atom are ligands –

– Metal = Lewis acid

– Ligand = Lewis Base

– Cu2+ + 4 :NH3 [Cu(NH3)4]2+

Lewis Lewis Coordination Complex

Acid Base

History

• Old compounds

– Prussian Blue – KFe[Fe(CN) 6]

– Aureolin – K3 [Co(NO2) 6]

– Alizarin red dye Ca2+ Al3+ salt of

– Teraamminecopper(II) ion [Cu(NH3)4(H2O)2]2+

Werner – Modern coordination theory

– Solve the bonding of [Co(NH3)6]Cl3

– Co is 3+ . How are the ammonias bonded?

– Bloomstrand = chain theory

– Werner = Coordination theory

Werner synthesized Isomers with no counterparts in chain theory.

Optically active D3 point group coordination complex

[Co(oxalate)3]3-

Werner’s optical D3 compound with no carbon atoms

Possible isomers of [Co(NH3)4Cl2]+ for various geometries

Four coordinate geometries of a Platinum complex

Skip Nomenclature 9.2

• Next few tables are common ligands

9.3 Isomerism

• Many types

• Stereoisomers – all bonds between same atoms. Different arrangements in space

• Structural or constitutional isomer – Some bonds are between different atoms.

• Diagram on next slide categorizes the types of compounds.

Stereoisomers – have same bonds but different arrangements in space.

• Four cordinate – Four coordinate MA2B2 square planar – cis and trans like cis-Platin and its isomer:

• Four coordinate MA2B2- square planar – cis and trans

• cis trans

Chirality

• Reminder: an object is chiral if it is not superimposible on its mirror image.

• Criteria – chiral object only have pure rotatations.

• Objects with improper rotations including i or σ or Sn are not chiral

Tetrahehral geometry

• Chiral for Mabcd (a,b,c, and d are monodentate ligand) similar to chiral carbon atoms

• Can be chiral with unsymmetric chelating rings

Such a a------b a and b are different donor atoms like HO-CH2-CH2-NH2

Square Planar Geometry can be chiral with asymmetrical chelates

Six coordinate complexes • Some isomers of the following compositions

may be chiral (a,b,c,d,e,f are monodentate ligands. Not all isomers of these composition are chiral

– [Ma2b2c2]

– [Mabc2d2]

– [Mabcd3]

– [Mabcde2]

– [Mabcdef]

Six coordinate complexes geometric isomers of [Ma3b3] and two tridentate ligands

Isomers for tetradentate ligands

Example Ma3bcd Total 5 isomer with one pair of enatiomers

• The 3 a ligands can be mer or fac .

• The mer configuration can have each of the 3 other ligands trans to the middle a ligand. This is three unique isomers. None of these are chiral because the plane containing a b c d in a plane of symmetry as shown in the first structure.

The other two isomers are enatiomers with the a ligands in the fac configuration this is a pair of emtiomers

Skip Sections 9.3.5, 9.3.6

Constitutional Isomers

• Have different bonded atoms

– Hydrate isomerism – Water is a ligand in one compound and an included solvent molecule in another. Ex. Isomers of CrCl3·6H2O

– (violet) [Cr(H2O)6]Cl3·

– (blue-green) [CrCl(H2O)5]Cl2·H2O

– (dark green) [CrCl2 (H2O)4]Cl3·2H2O

– (yellow-green)[CrCl3 (H2O)3]

Constitutional isomers (continued)

• Coordination isomers – ligands are bound to different metals

• Ex. [Co(en)3] [Cr(CN)6] and [Cr(en)3] [Co(CN)6]

or

[Pt(NH3)4] [PtCl6] and [Pt(NH3)4Cl2] [PtCl4]

Constitutional isomers (continued)

• Linkage isomerism – a ligand binds through two different atoms to a metal.

• Examples SCN- S bonding or N binding

• NO2- - N binding or O binding

• CN- - C binding or N binding

• Examples in Figures on next page:

Skip section 9.3.8

9.4 a survey of coordination numbers and structure

• Coordination number – number of ligands bound to the central atom

• Factors determining shape

– Coordination number

– VSEPR – main group mostly

– d electron occupancy (Chapter 10)

– Steric effects

– Crystal packing

Coordination number 1

• Rare, only with bulky ligands

Coordination number 2

• Rare, usually bulky ligands

• Some simple d10 complexes (see right side of figure) :

Coordination number 3

• Rare, usually bulky ligands or d10 like Au(I) or Cu(I).

Coordination number 3 (cont)

Coordination number 4

• Common, tetrahedral and square planar

• Tetrahedral is usually d10

Square Planar

• Usually d8 such as Ni(II), Pd(II), Pt(II) or Au(III)

Square Planar (cont)

Square planar (cont) This complex is square planar at 25 °C an tetrahedral at 80 °C

Coordination number = 5

• Less common than 4 or 6, but not rare.

• Trigonal bipyramid of square pyramidal. Energy difference often small

• Fe(CO)5 PF5 and have one NMR peak

• Some structure in the next few slides

Coordination number = 5

Coordination number = 5

Coordination number 6

• Very common, mostly octahedral some trigonal prismatic

• Octahedral may be elongated or compressed with certain d electron counts

Coordination number 6

(a) Trigonal prismatic (b) octahedral

Coordination number 6

Coordination number 6

Coordination number 7 and higher

• Less common

• 7 – pentagonal pyramid, capped trigonal prism, or capped octahedron,

•

Coordination number = 8

Coordination number 8

Coordination number 8

Coordination number greater than 8